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PubMed1976

[Round window membrane pathology in sudden deafness (author's transl)].

Exploration of the middle ear was performed on 15 patients with sudden deafness that had failed to improve after intravenous infusion of Eupaverin and Rheomacrodex. Three patients had abnormalities of the round window membrane, in 2 there was a perilymphatic fistula and in 1 an abnormal bulging of the membrane with no transmission of perilymphatic fluid movement. These 3 patients presented with a history of exertion or stress prior to the onset of symptoms. Surgical closure ofthe 2 fistulae led to improvement of hearing, and perilymphatic decompression in the third patient improved the tinnitus but not the deafness. The possible causes of round window pathology are discussed.

Acute Disease↗

PubMed1992

Enhanced horseradish peroxidase uptake in the electrically stimulated cochlea of the guinea pig.

Stimulation with alternating current at the round window causes an accelerated uptake of extracellular HRP by endocytotic vesicles in inner hair cells at the base of the stimulated cochlea, near the site of the electrode, but does not noticeably affect uptake into outer hair cells. After unilateral electrical stimulation, efferent endings on outer hair cells at the cochlear base show increased vesicular and endosomal labelling in both the ipsilateral and contralateral ears. It is concluded that round-window electrical stimulation increases afferent synaptic activity in inner hair cells near the electrode site, and also increases synaptic activity in OHC efferent endings, not only of the ipsilateral cochlea but also of the corresponding region of the contralateral cochlea. Rapid diffuse cytoplasmic labelling of inner and outer hair cells also occurs sporadically in both stimulated and unstimulated cochleae. However, in efferent terminals, diffuse labelling is restricted to stimulated animals, and occurs bilaterally, in corresponding basal regions of the cochlea.

Animals↗

PubMed1978

Round window niche melanocytes and webby tissue. Possible collateral route of vascular and perilymph circulation.

Two hundred thirteen human temporal bones were studied for characteristics of the round window niche. In 163 specimens melanocytes were found within the attachments of the round window membrane and in the niche, most prominently at the level of the cochlear aqueduct opening. Sixty-two specimens demonstrated discrete webby foci within the lining of the niche, 16 of which completely or partially covered the tympanic surface of the round window membrane, unassociated with fibrous tags or adhesions, and in some cases contained congested vascular channels and melanocytes. The webby foci were sometimes associate; with melanocytes, while melanocytes were present without demonstrable webby foci. These findings may represent a collateral route of vascular or perilymph-related drainage from the inner ear.

Adolescent↗

PubMed1992

[Solute movement across the round window membrane in comparison with that across the blood-labyrinth barrier].

The permeability of the normal round window membrane of the guinea pig to trimethylphenylammonium (TMPA) was assessed using ion-selective electrodes and compared with the rate of TMPA entry from the systemic blood circulation into the scala tympani (ST) of the cochlea across the so-called blood-labyrinth barrier. While the round window niche was irrigated with artificial perilymph containing 1 mM TMPA, the TMPA concentration in ST of the basal turn rose rapidly so as to reach 20-50% of the irrigating medium concentration in one hour. Following this procedure, the concentration declined significantly faster when the niche was subsequently irrigated with TMPA-free artificial perilymph than when the niche was left free of any fluid. This result shows that the membrane is fairly permeable to TMPA in both directions. Furthermore, TMPA entry from blood to STs of the basal and third turns was observed while the plasma TMPA concentration was maintained at about 0.5 mM by continuous intravenous infusion of isotonic 50 mM TMPA medium (1 part 150 mM TMPA + 2 parts lactated Ringer solution). TMPA appeared to distribute evenly from the blood to both turns at a much slower rate than across the round window membrane. In another experiment, the round window niche was irrigated with TMPA-free artificial perilymph during the intravenous infusion of 50 mM TMPA medium. The TMPA concentration increase in ST of the basal turn was greatly suppressed, whereas that of the third turn was not affected for at least an hour.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1983

Tympanostomy tubes and otic drops.

Otic drops have been proposed as a form of prophylaxis against the otitis media which follows middle ear contamination by water in patients with tympanostomy tubes. The potential adverse effects of this form of therapy were studied in chinchillas with tympanostomy tubes; 31 chinchillas underwent bilateral tympanostomy tube insertion. Seven animals had a mixture of green dye and Cortisporin otic suspension placed in both external auditory canals 24 hours following the placement of tympanostomy tubes and were sacrificed 30 minutes later for gross examination; 3 of these animals had previous eustachian tube obstruction with Silastic sponge. Twenty-one animals had Cortisporin otic suspension placed in the right external auditory canal on postoperative days 3, 4, 5, 6 and 7. No otic drops were placed in the left ear. Ten of these 20 animals had VIIIth nerve action potentials measured on postoperative day 17 and the other 11 animals had VIIIth nerve action potentials measured on postoperative day 42 followed by immediate sacrifice for histological examination and scanning electronmicroscopy. The remaining 3 animals had VIIIth nerve action potentials measured 21 days following tympanostomy tube insertion and served as electrophysiological controls. The 8 ears receiving Cortisporin otic drops mixed with green dye from animals with normal eustachian tubes showed staining of the round window membrane at sacrifice, while the 6 ears receiving Cortisporin otic suspension and green dye from animals with eustachian tube obstruction demonstrated no dye in the middle ear. All animals receiving Cortisporin otic drops in the right ear showed an intra-aural difference in action potentials with the right ear being attenuated by an average of 10.3 dB at 2,000 Hz, 12 dB at 4,000 Hz, 21 dB and 8,000 Hz, and 26 dB at 12,000 Hz. Morphological study revealed hair cell loss in the hook portion of the cochlea in those animals receiving Cortisporin otic drops. It was concluded from this study that, in patients with patent tympanostomy tubes in place, potentially ototoxic topical agents should be used with caution.

Action Potentials↗

PubMed1976

[Rupture of the round window membrane after slight head injury with flush of perilymph probably caused by large opening of aquaeductus cochleae (author's transl)].

A ringing deaf ear was noticed after slight head injury without loss of consciousness nor fracture of the skull. After performig tympanotomy a ruptured round window membrane with excessive flush of perilymph was found. We might rightly assume that this was induced by a large opening of aquaeductus cochleae combined with the force of inertia of the cerebral liquor and the direction of the push to the round window (blow behind the left ear).

Accidents, Home↗

PubMed1979

Round window ultrasonic irradiation: conservative surgery for Meniere's disease.

Ultrasonic irradiation of the labyrinth through the round window approach is a minimally destructive method of surgical management for Meniere's disease. Results of 48 procedures, followed from six months to eight years, are reported. Relief from vertiginous symptoms was obtained in 70 percent of the patients. Hearing was improved in 14 percent; hearing was also significantly worse in 14 percent. These findings resulted in an overall 56 percent of the patients falling into American Academy of Otolaryngology control classes A or B. No significant postoperative complications were observed. Results are difficult to classify on a cause-and-effect basis due to the remissions and exacerbations characteristic of Meniere's disease. Ultrasonic irradiation using the round window approach does not involve the potential risks of such surgical procedures as labyrinthectomy, vestibular neurectomy, and endolymphatic sac procedures. The primary disadvantage of this procedure is securing and servicing the instrumentation. Due to its conservative nature, ultrasonic irradiation through the round window is an attractive surgical consideration until such time when the pathologic processes in Meniere's disease are better understood.

Adult↗

PubMed1997

High jugular bulb and conductive hearing loss.

A high jugular bulb is often discovered as an incidental finding that is asymptomatic. Conductive hearing loss in association with this anomaly may occur, but has been reported infrequently in the literature. We report five cases of high jugular bulb and associated conductive hearing loss. Mechanisms to explain the conductive hearing loss include contact of the jugular bulb with the tympanic membrane, interference with the ossicular chain, and obstruction of the round window niche. The operative findings, radiographic and audiometric data that support these mechanisms of conductive hearing loss are presented.

Acoustic Impedance Tests↗

PubMed1992

[Vestibular evoked potentials. Diagnostic trends].

The contribution of short-latency evoked potentials to the exploration of auditory, visual and somatosensory neurosensory pathways is capital. The determination of short-latency vestibular evoked potentials has encountered many difficulties, mainly due to the necessity to find a specific, very short stimulation in order to select and synchronize the vestibular nerve fibers. Recent studies in animals have demonstrated short-latency potentials evoked by angular accelerations, linear accelerations or electric shocks on the round window. The generators of these potentials seem to be located in the vestibular nerve and nuclei. Electric stimulations of the internal ear have the advantage of providing a study of the peripheral vestibular pathways separately on both sides, while accelerations involve both vestibula, which probably makes the interpretation of data very difficult.

Acoustic Stimulation↗

PubMed1990

Summating potential/action potential ratio in perilymph fistula.

A prospective study of electrocochleography in patients with clinically suspected perilymph fistula was undertaken to determine its predictive value in that disorder. One hundred forty-four patients suspected of having perilymph fistula had electrocochleography performed--34 of these (39 ears) had exploratory tympanotomy. Of the 19 ears with normal preoperative summating potential/action potential (SP/AP) ratio, ten had perilymph fistula identified at the time of surgery. Of the 20 ears with abnormal SP/AP ratio, 16 had perilymph fistula confirmed at exploration, 18 had resolution of symptoms after oval window and round membrane grafting, and only one ear had postoperative persistence of the abnormal SP/AP ratio. This study suggests that an abnormal SP/AP ratio is not only predictive of endolymphatic hydrops, but also of perilymph fistula (both problems of inner ear fluid imbalance). This study also suggests that, while abnormal SP/AP ratio is fairly specific for inner ear fluid imbalance, it is not sensitive.

Adolescent↗

PubMedDate not supplied

Anatomical effects of sudden middle ear pressure changes.

Acute middle ear (ME) and inner ear changes following brief unilateral phasic ME pressure changes (up to +/- 6000/mm H2O) were studied in the guinea pig. Middle ear findings included perforation of the tympanic membrane, serous and serosanguinous exudate and hemorrhage of tympanic membrane and periosteal vessels. Changes were related to magnitude of applied pressure. Perforation and hemorrhage were more commonly seen with negative rather than positive pressure. Air bubbles behind the round window were seen with positive pressures. Occasional distortion, but never perforation of the round window, was noted. Hemorrhage of the scala tympani was observed with both positive and negative pressures; scala vestibuli hemorrhage was found with negative ME pressure. In some instances pressure direction and magnitude related changes were seen in the contralateral ear.

Animals↗

PubMed1981

Electrophysiological study of the maturation of auditory responses from the inner ear of the chick.

Three electrophysiological functions of the chick basilar papilla were studied during development by recording the compound actin potential (AP) at the round window. The auditory thresholds showed a continuous maturation between the fifteenth day of incubation (E15) and the first post-hatching day (P1), when they attained adult values. Responses matured first to low frequencies and later to high frequency stimuli. The input-output (intensity-amplitude) functions matured regularly and never demonstrated the classical two slopes seen in mammals. The tuning properties, studied by tone-on-tone masking of the AP, achieved mature values before the thresholds; the Q10s reached adult values at E17 for a 500-Hz probe tone and at E19 for a 1000-Hz probe tone. The fact that a low-to-high frequency development trend was found with the embryonic middle ear cleared of fluids further suggests that this property of auditory ontogeny may be a function of changes in the transduction properties of the cochlea.

Aging↗

PubMed2001

Perilymphatic concentration of gentamicin administered intratympanically in guinea pigs.

Intratympanic gentamicin therapy has recently become popular for Meniere's disease, although the administration protocol remains controversial. To date, few studies have been conducted regarding the pharmacokinetics of drugs administered intratympanically. We measured gentamicin concentration in the perilymph close to the round window membrane using a microdialysis technique. A bolus of 0.5 mg gentamicin was put on the round window membrane or a clinically used solution of 5 mg gentamicin was placed in the tympanic bulla of guinea pigs. After 56 +/- 21 min of bolus administration, gentamicin concentration reached a maximum level of 2900 +/- 1200 microg/ml and then decreased, with a half-life of 117 +/- 47 min, characteristic of the kinetics expected with a one-compartment model. With solution administration, the maximum concentration did not differ, but the time to the maximum concentration and the half-life in the perilymph were longer, compared with the results of bolus administration. Our results suggest that even solution administration of gentamicin, which is simple and repeatable, provides a sufficient, stable and continuous supply to the perilymph.

Animals↗

PubMed1994

Comment on "Modulation of the hair cell motor: a possible source of odd-order distortion" [J. Acoust. Soc. Am. 96, 2210-2215 (1994)].

This reply to the response by Brown [J. Acoust. Soc. Am. 96, 2210-2215 (1994) on the report "Intermodulation distortion (F2-F1) in inner hair cell and basilar membrane responses [J. Acoust. Soc. Am. 93. 2061-2068 (1993)]" by Nuttall and Dolan is for the purpose of adding additional data concerning the nature and origin of the round window (RW)-recorded quadratic distortion tone (QDT) signal. It is shown that a major portion of the RW electrical signal originates from the activity of auditory neurons since tetrodotoxin (TTX) applied to the cochlea diminished the distortion product by about 75%. The neural component is also responsible for the characteristic 900-Hz optimal frequency separation of the primaries in producing the response. These data support our earlier suggestion [Nuttall and Dolan, J. Acoust. Soc. Am 93, 2061-2068 (1993)] that the level of intracellular receptor potential at the QDT frequency would be a stimulus for afferent fibers at low sound levels. These new data do not force a reinterpretation of Brown's hypothesis on the relationship of quadratic and cubic intermodulation distortion.

Ear, Inner↗

PubMed1998

Improvement in inner ear blood flow by nitric oxide following experimentally induced cochlear thrombosis in anesthetized guinea pigs.

The nitric oxide (NO) donor sodium nitropruside (SNP) applied to the round window membrane has recently been found to increase cochlear blood flow (CoBF) in normal guinea pigs and in normal and presbyacusic mice. This study examined the effect of topical applications of SNP on experimentally impaired CoBF in anesthetized guinea pigs. Small (3 microliters) portions of 3% SNP were applied to the round window niche of both normal and thrombosed cochleas. Local vascular impairment was produced by ferromagnetic thrombosis of cochlear blood vessels and the microcirculation measured using laser Doppler flowmetry. Ferromagnetic thrombosis resulted in a mean decrease of CoBF to 52% of baseline. There was a clear improvement in mean CoBF to 84% of baseline by the topical application of SNP that depended on the degree of ischemic damage produced. Under neuroleptanalgesia and ketamine-xylazine anesthesia, significant increases in CoBF were measured in normal ears as well as in the thrombosed ones. However, several SNP applications were needed to improve the impaired CoBF, while a single portion was sufficient in the normal cochlea to cause a drastic increase in mean CoBF to 234% of baseline. In urethane-anesthetized animals, no flow increase was found despite repeated drug administration. Careful evaluation of the laser Doppler signals was necessary to accurately determine the concentrations of the moving blood cells and their mean velocities.

Administration, Topical↗

PubMed1994

Epinephrine-induced changes in human cochlear blood flow.

Cochlear blood flow (CBF) was monitored over the basal turn stria vascularis using laser Doppler flowmetry in five human subjects during middle ear surgery. The effects of systemically administered epinephrine (0.3 microgram/kg) and topically applied epinephrine (1:10,000) on the round window membrane (RWM) were examined. Topical epinephrine caused a mean reduction of 60 percent in CBF (maximum peak reduction 65-85% across subjects), which slowly recovered ( > 10 min) toward baseline following epinephrine removal from the RWM. The changes in CBF are similar to those found in animal studies, but are much larger, indicating a relatively more pronounced role of adrenergic agents in CBF control in humans. Systemic epinephrine caused a 40 percent decrease in skin blood flow, a 90 percent increase in blood pressure (BP), above a resting hypotensive mean level of 65 mmHg, and a 50 percent increase in CBF. The CBF change followed the change in BP, but recovered toward baseline more slowly. The dramatic and somewhat prolonged decreases in CBF with RWM application of epinephrine may compromise sensory function and could account for the occasional unexplained sensorineural hearing loss or tinnitus associated with middle ear procedures that use topical epinephrine. The semipermeability of the RWM may, on the other hand, offer a route for therapeutic increases in CBF with vasodilative agents and provide an appropriate treatment for some cases of sensorineural hearing loss.

Administration, Topical↗

PubMed1999

Use of a new device, the MicroWick, to deliver medication to the inner ear.

A new procedure for delivering medication directly to the inner ear has been developed. This delivery system, called the MicroWick, involves the use of a small wick that is inserted through a tympanic membrane vent tube into the round window niche. Once the wick has been inserted, the patient can self-administer eardrops into the ear canal, where they are absorbed by the wick and transported to the round window membrane and to the inner ear fluids. Inserting the wick is a minor procedure that is performed in the office. This paper describes the indications for and use of the MicroWick.

Anti-Bacterial Agents↗

PubMed2004

Long-term results of gentamicin inner ear perfusion in Ménière's disease.

Chemical perfusion of the inner ear is an increasingly popular treatment for Ménière's disease. The authors report on the long-term results of 22 patients treated with gentamicin delivered via a round window micro-catheter. Patients with Ménière's disease underwent continuous, low dose (10 mg/ml) gentamicin infusion at 5 microlitre per hour for 10 days, through a micro-catheter placed into the round window niche. Vertigo was controlled in 95 per cent, whilst preserving hearing in 77 per cent. Hearing improved in three patients. Three patients with pre-operative serviceable hearing (PTA < 50 db) demonstrated reduced hearing; two patients with pre-operative non-serviceable hearing developed a dead ear. Tinnitus and aural fullness remained unchanged or improved in 86 per cent and 68 per cent respectively. Long-term vertigo control can be achieved using low dose gentamicin, whilst preserving hearing and vestibular function in the majority of patients. This procedure appears to stabilize the vestibular function, enhancing the chance of effective vestibular rehabilitation.

Administration, Topical↗